Generalize deep nested array setExistingOffsetValueType for arbitrary depth

The previous fix only handled 3-level nesting by checking that inner
value types were constant arrays. For 4+ levels, the intermediate
value types are general ArrayTypes, so the condition failed.

Generalize the condition to recurse through any depth of array nesting:
- Check both types are non-constant arrays (constant arrays are handled
  by the existing block above)
- Check both types' value types are arrays (ensuring there's deeper
  nesting structure to recurse into, excluding generic arrays like
  non-empty-array whose value type is mixed)

The recursion naturally bottoms out when it reaches constant arrays
at the deepest level.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Type/ArrayType.php

@@ -412,9 +412,11 @@ public function setExistingOffsetValueType(Type $offsetType, Type $valueType): T
 
 		if (
 			$this->itemType->isArray()->yes()
+			&& !$this->itemType->isConstantArray()->yes()
 			&& $valueType->isArray()->yes()
-			&& $this->itemType->getIterableValueType()->isConstantArray()->yes()
-			&& $valueType->getIterableValueType()->isConstantArray()->yes()
+			&& !$valueType->isConstantArray()->yes()
+			&& $this->itemType->getIterableValueType()->isArray()->yes()
+			&& $valueType->getIterableValueType()->isArray()->yes()
 		) {
 			$newItemType = $this->itemType->setExistingOffsetValueType(
 				$valueType->getIterableKeyType(),

tests/PHPStan/Analyser/nsrt/bug-13637.php

@@ -24,6 +24,26 @@ function doesNotWork() : array {
 	return $final;
 }
 
+/**
+* @return array<int, array<int, array<int, array<int, array{abc: int, def: int, ghi: int}>>>>
+*/
+function fourLevelsDeep() : array {
+	$final = [];
+
+	for ($i = 0; $i < 5; $i++) {
+		$j = $i * 2;
+		$k = $j + 1;
+		$l = $i * 3;
+		$final[$i][$j][$k][$l]['abc'] = $i;
+		$final[$i][$j][$k][$l]['def'] = $i;
+		$final[$i][$j][$k][$l]['ghi'] = $i;
+
+		assertType("array{abc: int<0, 4>, def: int<0, 4>, ghi: int<0, 4>}", $final[$i][$j][$k][$l]);
+	}
+
+	return $final;
+}
+
 /**
 * @return array<int, array<int, array{abc: int, def: int, ghi: int}>>
 */